Pyrotechnic devices

ABSTRACT

In a rocket with plastic propellant, which includes a solid oxidizing agent, a fuse means is used to directly ignite the propellant, and copper chromate is associated with the propellant by either being distributed within the propellant and/or on the surface of the propellant to be ignited.

Unite II States Patent I 1 I 1 3,715,984

Murray Feb. 13, 1973 I541 PYROTECHNIC DEVTCES 478,623 7/1892 Marston 102 324 Inventor: Dudley Charles y, Homing 3,551,225 12/1970 Sayles ..l49/76 X Ion, England FOREIGN PATENTS OR APPLICATIONS [73] Assign: pains'wesse" Salisbury 268,462 3 1951 Switzerland"... ..l02/34.2

Wiltshire, England [22] Filed: June 9, 1970 Primary Examiner-Benjamin A. Borchelt Assistant Examiner-D. A Bent [21] Appl' 44725 Attorney-Hall & Houghton [3()] Foreign Application Priority Data [57] ABSTRACT June 9, 1969 Great Britain ..28,974/69 In a rocket with plastic propellant, which includes a solid oxidizing agent, a fuse means is used to directly [52] US. Cl ..l02/34.2, 149/19 ignite the propellant, and copper chromate is as [5 1] Int. Cl. ..C06d 1/04, CO6!) 19/02 sociated with the propellant by either being dis- [58] Field of Search lO2/34.2, 37.4; l49/l9 tributed within the propellant and/or on the surface of the propellant to be ignited. [56] References Cited 13 Claims, 2 Drawing Figures UNITED STATES PATENTS 3,255,281 6/1966 Alexander ..l49/l9 PATENTEDFEB 13 I973 FIG. If

l 00LE7 URRU1X INVENTOR ATTORNEY PYROTECHNIC DEVICES This invention relates to pyrotechnic devices, and especially to rockets propelled by the combustion of gas-producing compositions which are plastic and so can be easily shaped during manufacture.

Although the use of plastic propellants facilitates the manufacture of pyrotechnic devices in which they are incorporated and has advantages arising from the fact that they do not develop internal stresses during expansions or contractions induced by temperature changes, they have been found to require relatively high temperatures for ignition. In large rockets, in which electrically fired pyrotechnic igniters are generally used, this has not given rise to any substantial difficulty, but dif ficulties do arise in the case of small rockets of the kind suitable for being tired from the hand, because it is often inconvenient or impracticable to provide electrically fired pyrotechnic igniters, that is to say, a pyrotechnic igniter substance which is ignited electrically and which in turn ignites the propellant, in such rockets.

The present invention is based on the observation that certain plastic propellants can easily and reliably be ignited directly with quickmatch or like combustible material, for example, primed cambric, that is to say, without the use of a pyrotechnic igniter substance which is itself ignited by the quickmatch or like combustible material and which in turn ignites the propellant.

The present invention provides a rocket comprising a combustion chamber, a mass of propellant, and a fuse means consisting of quickmatch or like combustible material arranged to ignite the propellant mass directly, wherein the propellant is a plastic gas-producing composition which includes a solid oxidizing agent, the composition being bound together by a polymeric aliphatic hydrocarbon having side groups and which is a visco-elastic liquid having a viscosity in the range of from 250,000 to 7,000,000 poises at 25 C, and there being copper chromate associated with the propellant.

The copper chromate associated with the propellant may be distributed within the propellant mass and/or exposed on at least part of the propellant surface that is to be ignited.

The fact that no conventional igniter substance is used in conjunction with the quickmatch or like combustible material avoids the difficulties associated with providing such an igniter substance.

Advantageously, there is copper chromate exposed on at least part of the propellant surface that is to be ignited.

Advantageously, copper chromate is distributed discontinuously over the whole of the exposed propellant surface, that is to say, the distribution is not such that a continuous layer of copper chromate covers the surface and completely masks the propellant. Such a discontinuous distribution ensures that, on ignition, the flame front spreads uniformly over the propellant surface. Although it is in general advantageous for there to be a discontinuous distribution of copper chromate over the whole of the exposed propellant surface, it will be sufficient in many cases merely to arrange that there is a discontinuous layer of copper chromate on the propellant surface in the region where it is desired that initial ignition should occur.

The presence of copper chromate exposed on the propellant surface is especially useful in cases where an exuded barrier layer of the visco-elastic liquid binder has formed on the surface as a result of the propellant composition having been consolidated under pressure. Such a layer, which may retard or inhibit ignition of the propellant, is especially likely to form when the composition contains a relatively high proportion of the binder.

The layer of binder may act as a thermal insulator or otherwise inhibit ignition or retard the spread of the flame front and, in consequence, the rate of evolution of gas from the propellant may be insufficient to allow uniform combustion to be maintained, and the rocket may self-extinguish.

Copper chromate may be applied to the propellant surface in a variety of ways. Thus, for example, the copper chromate can be applied by a dusting or sprinkling treatment, the solid particles being held on the surface by the mild adhesive action or tack" of the binder. Alternatively, the copper chromate may be applied in the form of a slurry in a volatile liquid, the liquid then being allowed or caused to evaporate. It is desirable to use a volatile liquid which is a solvent capable of dissolving the binder, for example, petroleum ether, as the action of such a solvent results in the copper chromate particles being embedded more firmly in the propellant surface. It is sometimes advantageous, where the copper chromate is to be applied to the propellant surface in a slurry in such a solvent, to increase the viscosity of the solvent by dissolving small quantities of a visco-elastic material therein, for example, to give a 0.5 to 5 percent solution. An ex ample of a suitable visco-elastic material is the high molecular weight polyisobutene known as OPPANOL B 150.

It is important that the thickness of any layer of copper chromate applied to the propellant surface should not be too great, as such a layer may act as a thermal insulator and so retard or inhibit ignition. In general, the quantity of copper chromate applied to the propellant surface should be less than that which would be required in order to form a continuous layer.

Advantageously, the particle size of the copper chromate is such that substantially all of it will pass through a mesh (B.S.S.) screen.

Instead of, or, advantageously, in addition to there being copper chromate exposed on the propellant surface, copper chromate may be distributed throughout the propellant mass. Advantageously, the gas-producing composition is an intimate mixture of constituents including at least 0.5 percent by weight of copper chromate. Preferably, the gas-producing composition includes from 1 to 2 percent by weight of copper chromate. It will generally be found that little or no advantage is gained by using proportions of copper chromate above about 2 percent by weight.

When a propellant is used which includes a quantity of copper chromate distributed throughout its mass, there will, usually, be copper chromate present in the surface to be ignited and, in general, little or no advantage will then be gained by applying additional copper chromate to the surface. As is explained hereinbefore, however, there may be an exuded layer of binder on the propellant surface, and it is desirable in such cases to apply copper chromate to the surface, for example, by a dusting or sprinkling treatment, in order to ensure that there is sufficient copper chromate at the surface to facilitate ignition. Alternatively, it may be possible to expose copper chromate particles embedded in the propellant mass by dissolving at least part of the exuded layer by means of a suitable solvent.

Quickmatch is a well-known combustible material usually consisting of cotton which has been treated with a suspension of sulphurless mealed powder in gum arabic or starch solution. Sulphurless mealed powder comprises about 70 percent by weight of potassium nitrate and about 30 percent by weight of charcoal, and the particle size of the powder is usually such that substantially all of it will pass through a 240 mesh (B.S.S.)

screen.

The quickmatch or like combustible material may be ignited by any suitable means, for example, by a flash from a cartridge cap or Bickford fuse.

It is not essential for any portion of the quickmatch or like combustible material to be in contact with the propellant.

Advantageously, the quickmatch or like combustible material extends through the nozzle of the rocket and terminates close to an exposed surface of the propellant mass. Preferably, the exposed surface is a surface of which at least a part has copper chromate exposed thereon. The point at which the quickmatch or like combustible material terminates will depend upon the configuration of the propellant mass and upon where it is desired that initial ignition of the propellant mass should occur. Thus, for example, the quickmatch or like combustible material may terminate adjacent to the rear end of the propellant mass, or may pass into or through a bore in the propellant mass and terminate either within the bore or at a point outside the propellant mass and adjacent to the front end thereof.

The quickmatch or like combustible material may be self-supporting or there may be provided support means, for example, a tube surrounding the quickmatch or like combustible material. The tube may be constructed of a plastics material, paper, or metal. The presence of a tube around the quickmatch or like combustible material greatly increases the rate of travel of the igniting flame.

Preferably, the solid oxidizing agent in the plastic gas-producing composition is ammonium perchlorate.

The visco-elastic liquid binder is preferably polyisobutene. In order to improve the action of the binder, a small quantity of a surface-active agent may be incorporated in the plastic gas-producing composition. Preferably, the surface-active agent is a mixture of at least two organic compounds of which at least one is an organic sulphate, an inorganic salt of an esterified dibasic sulphonated acid, or an ester of a long chain fatty acid. Advantageously, the proportion of the sur face-active agent in the gas-producing composition is about 1 percent by weight.

The propellant composition may also include a moderating agent such as, for example, ammonium picrate or oxamide.

Further information concerning plastic gas-producing compositions suitable for use as the propellant in accordance with the invention may be found in United Kingdom Patent Specification No. 915,910.

The following are two examples of plastic gasproducing compositions suitable for use in accordance with the invention, all the percentages being by weight:

I. Ammonium perchlorate 84.5% Polyisobutene 12.5% Surfaceactive agent 1% (Pentaerythritol dioleate 30% Ethyl oleate 40% Sodium dioctyl sulphosuccinate 30%) Copper chromate 1% ll. Ammonium perchlorate 85.5% Polyisobutene 12.5% Titanium dioxide 1.0% Surface-active agent 1.0%

Two forms of rocket motor constructed in accordance with the invention will now be described by way of example with reference to the accompanying drawings in which:

FIG. 1 shows an axial section of one form of rocket motor; and

FIG. 2 shows an axial section, on a smaller scale than FIG. 1, of a second form of rocket motor.

Referring to FIG. 1 of the accompanying drawings, the first form of rocket motor comprises a generally tubular rocket casing, a part of which is indicated by the reference numeral 11. A generally cylindrical combustion chamber, which is indicated by the reference numeral 2, is located against axial movement within the rocket casing 1 by means of waists 3 and 4 formed in the rocket casing. A nozzle member 5 is provided at the lower end of the combustion chamber 1, and the upper end wall of the combustion chamber is formed with a tubular extension 6 of reduced diameter. The extension 6 provides communication with an upper chamber of the rocket (not shown) which may contain a signal composition such as, for example, a flare-producing or smoke-producing composition. The extension 6 contains a fuse composition 7. v

A mass of propellant 8, which is a plastic gas-producing composition as hereinbefore defined, fits tightly within the combustion chamber 2. The length of the propellant mass 8 is less than the internal length of the combustion chamber 2 and there is thus a gap between the nozzle member 5 and the nearer end of the propellant mass.

A quickmatch 9 extends from a firing device 10 through the aperture in the nozzle member 5 and terminates at the base of a recess 11 formed in the rear end portion of the propellant mass 8. The recess 11 is provided with a discontinuous surface coating of copper chromate.

In operation, the firing device 10 ignites the quickmatch 9 which burns along its length and in turn ignites the propellant mass 8. The gas which is produced by combustion of the propellant provides the motive force for the rocket. In due course, the burning propellant mass ignites the fuse composition 7, which in turn ignites the signal composition.

Referring to FIG. 2 of the accompanying drawings, the second form of rocket motor comprises a cylindrical combustion chamber which is indicated generally by the reference numeral 12. A nozzle member 13 is provided at one end of the combustion chamber. A closure member 14, which is located against axial movement by a waist 115, forms the other end wall of the combustion chamber.

A hollow cylindrical propellant mass 16 fits tightly 0. means for igniting said propellant comprising the inside the combustion chamber 12 and the hollow incombination of terior of the propellant tapers outwardly towards each iii. copper chromate associated with the propellant end of the chamber, that is to say, the hollow interior of in the region where it is desired that initial ignithe propellant mass is frusto-conical in shape towards 5 io Occur, and each end of the chamber. The propellant is a plastic fuse means f quickmatch material having a gas-producing composition as hereinbefore defined. A Portion thereof j PO d to the propellant in strand of quickmatch material, which is indicated schesald region for igniting tha Same directly with matically by the dotted line 17 in FIG. 2, extends from the aid of Said pp chromateoutside the nozzle member 13 through the hollow in- A "Q according to f 1, wherein least terior of the propellant mass and is surrounded along P of sald copper chliomate faxposed 9 f P of the greater part of its length by a paper tube 18 The the propellant surface ln the region to be ignited. I

' tube terminates near a disc of primed cambric A Focket F F Q to clam] wherem there a quickmatch material 19 which is located parallel to the dlsmbltwn F exPosed closure member 14 at the base of the frusto-conical in- 15 over substantlauy the Whole of h sald terior of the propellant mass. The surfaces of the A rocket F l to Clam wheremlhg sald frusto-conical interior of the propellant mass, which Surface hasasprmklmg copper ihromate thelieon' are indicated by the reference numerals and 21, are A rocket a.ccordmg Cllum wherem sald provided with a discontinuous surface coating of g f gl fi ofa pfimclehslzelszuch a copper chromate. The quickmatch strand 17 extends 20 Ha y a O n pass t mug a 0 mes screen. gr i l tube 18 and termmates near the primed 6. A rocket according to claim 1, wherein the said binder com risesa ol isobutene. In operation of the rocket motor shown in FIG. 2, the 7 A l g di to l i 1 h i h id strand 17 is ignited by any suitable means, for example, composition includes from 1 to 2 percent by weight of by means of the flash from a cartridge cap. The strand said copper chromate.

then burns rapidly along its length and ignites the 8. A rocket according to claim 1, wherein the said primed cambric 19 which in turn ignites the propellant plastic gas-producing composition has admixed therein 16. at least 0.5 percent by weight of said copper chromate.

The tube 18 serves to shield the propellant from the 9. A rocket according to claim 8, wherein at least flame travelling along the quickmatch strand 17 and so part of said copper chromate is exposed on a portion of ensures that ignition of the propellant by the the propellant surface in the region to be ignited. quickmatch material 17, 19 occurs initially towards the A rocket according to claim 8, wherein there is a front end of the combustion chamber. discontinuous distribution of copper chromate over I claim: substantially the whole of the said surface.

1, A rocket om ri i 11. A rocket according to claim 8, wherein the a combustion h b propellant mass has a sprinkling of copper chromate b. a mass of propellant located within said chamber, thereonsaid propellant being a plastic gas-producing co 12. A rocket accordmg to clalm 8, whereln the partlposition and Said composition comprising; cle slze of the copper chromate is such that substani. asolid oxidizing agent and tlally all of It will pass through a 120 mesh (B.S.S.) ii. a binder which is a visco-elastic liquid comprisscreenl ing a po|ymeric aliphatic hydrocarbon having 13. A rocket accordlng to clalm 8, wherein the sald side groups and a viscosity in the range of from bmder compnses a polylsobutene- 250,000 to 7,000,000 poises at 25 C.; and 

1. A rocket comprising: a. a combustion chamber; b. a mass of propellant located within said chamber, said propellant being a plastic gas-producing composition and said composition comprising: i. a solid oxidizing agent and ii. a binder which is a visco-elastic liquid comprising a Polymeric aliphatic hydrocarbon having side groups and a viscosity in the range of from 250,000 to 7,000,000 poises at 25* C.; and c. means for igniting said propellant comprising the combination of iii. copper chromate associated with the propellant in the region where it is desired that initial ignition occur, and iv. fuse means of quickmatch material having a portion thereof juxtaposed to the propellant in said region for igniting the same directly with the aid of said copper chromate.
 2. A rocket according to claim 1, wherein at least part of said copper chromate is exposed on a portion of the propellant surface in the region to be ignited.
 3. A rocket according to claim 2, wherein there is a discontinuous distribution of copper chromate exposed over substantially the whole of the said surface.
 4. A rocket according to claim 2, wherein the said surface has a sprinkling of copper chromate thereon.
 5. A rocket according to claim 1, wherein said copper chromate is of a particle size such that substantially all of it will pass through a 120 mesh (B.S.S.) screen.
 6. A rocket according to claim 1, wherein the said binder comprises a polyisobutene.
 7. A rocket according to claim 1, wherein the said composition includes from 1 to 2 percent by weight of said copper chromate.
 8. A rocket according to claim 1, wherein the said plastic gas-producing composition has admixed therein at least 0.5 percent by weight of said copper chromate.
 9. A rocket according to claim 8, wherein at least part of said copper chromate is exposed on a portion of the propellant surface in the region to be ignited.
 10. A rocket according to claim 8, wherein there is a discontinuous distribution of copper chromate over substantially the whole of the said surface.
 11. A rocket according to claim 8, wherein the propellant mass has a sprinkling of copper chromate thereon.
 12. A rocket according to claim 8, wherein the particle size of the copper chromate is such that substantially all of it will pass through a 120 mesh (B.S.S.) screen. 